Strathclyde police said on Friday they were taking over responsibility for security at Olympic venues in Glasgow from G4S as concerns continued over the firm's staff shortages.

The police force said it was taking over "primary responsibility for security at Olympic venues" including the Hampden Park football stadium.

Greater Manchester Police (GMP) also confirmed it was to send a small team of officers to Manchester United's Old Trafford stadium, where mens' football matched are scheduled to take place.

It came as the national Olympic security co-ordinator, Metropolitan police assistant commissioner Chris Allison, said that increasing numbers of police officers may be called up to help with security as the start of the games on 27 July gets closer.

"Extra officers will be deployed to these operations. However, this will have no impact on the level of service in our communities.

"At this time we do not anticipate that there will be any need for military involvement."

GMP assistant chief constable Terry Sweeney said its decision to send specialist officers to games at Old Trafford came after discussions with Locog.

"The decision was taken as part of GMP's contingency planning process and will ensure a significant police presence is in place at the stadium for the duration of the Olympic football matches," he said.

"The officers will be in place from Sunday and at no point has this move changed the security arrangements for the athletes."

The drafting in of extra police officers comes on top of the additional 3,500 troops who are being brought in after G4S admitted it was struggling to recruit enough security guards.

The number of military personnel involved in Olympics security is now 17,000, including 11,000 who will help secure Games venues, with the rest working in specialist roles.

A further 1,200 are on 48 hours notice to move.

AC Allison said that the number of police officers working on Olympic-related duties varied from force to force and "is constantly subject to change to ensure security is properly maintained".

"As we get increasingly close to the venues opening and sport being played, this support may involve deploying police officers in greater numbers," he said.

Three police forces are considering abandoning a multimillion-pound contract with G4S following the firm's Olympic security failings.

The chief constables of Cambridgeshire, Bedfordshire and Hertfordshire police met on Thursday to discuss plans to switch 1,100 back-office posts to the security contractor.

They will hold a behind-closed-doors meeting with police authority members on Monday to further discuss the plans.